In digital video technology, systems have long been provided for capturing or digitizing analog still images in various formats such as composite video or RGB. Such capturing may typically take the form of a live capture in which the image is fully digitized as it is received, and a second category wherein the capturing process is distributed over time and may include components derived from several frames of video data.
An example of the latter is sequential RGB capture, the disadvantage of this latter category being that in order to avoid blurred images, the target must remain relatively stationary during capture. However, the problem presents itself of generating unintentional motion video even for live capture of a relatively still image from an interlaced video signal. In interlace video which is conventional in video technology, a single image or frame is actually composed of two images, or fields taken 1/60 second apart, for example. The first image might contain even numbered scan lines with the second image being odd numbered scan lines inserted or interlaced between the even scan lines after display of the first image, much like the interlacing which occurs in the shuffling of a deck of cards. An example of this interlace form of scanning may be found in conventional broadcast television raster scan images.
As aforementioned, a problem occurs with a non stationary target presented to the capture camera wherein these two fields adjacent in time are captured--even when the sequential capturing occurs 1/60th of a second apart. As a practical example, if a subject were to move a hand during the capturing process, sequential fields will be generated which will capture the hand in two distinctly different positions. However, operation of typical interlace systems call for the two fields to be continuously refreshed alternately on the display screen. The result of this may be the appearance of the hand engaged in a jittering or shaking motion at the frequency of 30 times a second giving rise to highly undesirable images.
In an effort to avoid this problem systems were developed which discarded all the scan lines associated with one of the alternating fields. The obvious undesirable result of this was of course a substantial decrease in resolution of the image, an example of which may be readily seen with respect to consumer video cassette recorders. Most such video tape players include a freeze frame mode. Due to mechanical limitations on video heads and the like, this mode displays a single field of 240 scan lines, which is only half of the 480 scan line frame attributed to consumer video. This is perceived by the view or as a substantial reduction in image quality from the full resolution image on the videotape prior to freeze frame playback.
For all of the foregoing and other reasons, a system and method was highly desired for providing an enhancement to video image capture and display systems which could eliminate motion artifacts such as undesirable image shaking of fast moving components and the like from the captured image while at the same time retaining most of the resolution of the full interlaced image.